A thermal processing apparatus and a thermal processing method where the vessel with interconnected chambers in which the solid material is thermally processed is suspended in a heat exchange medium while it is rotated, which reduces the energy to rotate the vessel, increases heat transfer surface area, increases the turbulence of the heat exchange medium around the vessel and improves the movement of solid particles relative to each other and relative to the heat exchange surface. These features combine to increase the heat transfer rates within a compact vessel size.